SA-9900 Output transistors + Refurb help

[sajjad amer]

I have been victim of a seller on eBay and bought what I thought was a working 9900. However although it "works" in strict sense, all caps are swollen and output transistors are all different and Wire from pin 6 of protection circuit is also missing.
Essentially it looks like dogs dinner and I cannot contact the seller , reported to eBay.
Original output transistors should have been 2SA679/2sc1079 , what are the modern day replacements for them?
I will upload pictures shortly.

 

[sajjad amer]

Pictures

 

[glen65]

2SA679 use MJ21193G
2SC1079 use MJ21194G

What you have is definitely hacknological victim. From the pic, it looks like they just threw an insulator under those TO3Ps and only used the original paste. It doesn't look like they even used any between the device and insulator from this vantage point. All of those outputs should be pulled, all heat sink surfaces thoroughly cleaned and then replaced

 

[sajjad amer]

@glen65 thank you , would you agree that all outputs should be replaced or should I leave them be. I have found the transistors you suggested in UK and wanted to ask experts before I jump right in.

 

[johnlcnm]

Sajjad. I guess I have been lucky on my amp purchases so far. I try to look close at the top cover if the photo is good enough. Look for any evidence of screwdriver slippage in the phillips slots. Unmolested pieces of equipment are the best!

 

[glen65]

@glen65 thank you , would you agree that all outputs should be replaced or should I leave them be. I have found the transistors you suggested in UK and wanted to ask experts before I jump right in.

Yep, get rid of them. Reusing those would likely just end up causing problems, not worth it.

 

[sajjad amer]

Need more help please

1. There are 2 jumper wires connecting pin 23 and 13 , 21-16 --- should I remove them? What's their purpose here
2. There is a diode on the board should it be there or it should be removed

Cable from pin 3 has been cut where should it go? I can not decipher schematic all lines are crossing each other.

 

[glen65]

What a mess,
If you're having difficulty reading the schematic maybe a different service manual will help.
https://www.hifiengine.com/manual_library/pioneer/sa-9900.shtml

Your board has a couple of burnt emitter resistors. Looks like they are the wrong value and maybe the wrong wattage as well. Also they replaced 1/4 watt carbon film resistors, with what looks like 2 watt metal oxide. So they used a replacement that's way too big. I'm including a pic of an amp board that's all original which you can use as a visual reference.

 

[markthefixer]

The replacement transistors and parts you procure should be sourced from a reputable industrial dealer, both for the reduced potential of counterfeits and freshness of components.

 

[sajjad amer]

Thank you both for guidance. I'm getting parts from digikey US and RS components in UK.
The jumpers I mentioned above should I remove them? There is no break on PCB and it's checking fine on continuity.
Also the diodes on the back of board should they still be there?
I have superficial knowledge of electronics and am concerned that previous person may have made some changes upstream and to compensate he may have made these modifications to AWH037? Please guide me

 

[LesE]

AWH-037-A pin 23 is +58V (unregulated) and pin 13 is +58V (regulated). Pin 21 is -58V (unregulated) and pin 16 is -58V (regulated). The regulated and unregulated power supplies should not be connected together. I suspect that the regulated power supply may have failed and instead of performing a proper repair, they tied all of the +/- 58V pins to the unregulated supply. However, that's just a guess.

The diodes attached to the foil side of the board were added on and it's difficult to know what the reason may have been. This power amplifier board needs to been gone through with a fine tooth comb with every component tested and rebuilt with proper components.

The AWR-077 power supply board has also been modified. There shouldn't be any transistors mounted on the foil side of the PCB. You will want to make sure that the amplifier hasn't been rewired so that the AWR-077 is providing +/-48V where it should be provided by the AWR-070.

Pin 6 on AWM-071 protection assembly should be connected to pin 18 on AWH-037 amplifier. AWM-071 should also be rebuilt. All wiring into the AMW-071 should be verified.

The AWR-070 power supply should be tested and rebuilt as required. Needless to say, this amp should only be powered up on a DBT until all of the issues are corrected.

 

[Unjoy]

The diodes on the foil side may have been added to cover up for non-functioning (or absent) STV3H diodes. Check them out as well, I don't recognize the components with the isolated wires and lugs on the bottom of your pcb's as being STV3H's?

 

[sajjad amer]

@LesE I am glad that you responded.
I am using your part list to build this whole amplifier up board by board. Your list was last updated 13 May 2017, I hope there are no changes to this?
Many Thanks
Sajjad

 

[LesE]

@LesE I am glad that you responded.
I am using your part list to build this whole amplifier up board by board. Your list was last updated 13 May 2017, I hope there are no changes to this?
Many Thanks
Sajjad

Actually, I have recently withdrawn the list for review of the Switch, Control and Protection assembly replacements. It should be safe to proceed with the power amp and power supply lists.

 

[sajjad amer]

The diodes on the foil side may have been added to cover up for non-functioning (or absent) STV3H diodes. Check them out as well, I don't recognize the components with the isolated wires and lugs on the bottom of your pcb's as being STV3H's?

I did not know what is STVH, googled it , those things are on the board and were connected to the heat sink with screws. So I will remove these diodes and continue to rebuild the board. Thank you

 

[Goldie99]

Hi Sajjad, that's bad luck with the eBay purchase - if it's the one I think it is, the internal condition & repairs (for want of a better word) certainly weren't obvious from the listing description.

You might find the following link is a better, more legible, copy of the service manual - http://www.kallhovde.com/pioneer/sa-9900smhires.pdf

A couple of other reliable UK based suppliers would be CPC, Farnell, and eventually Cricklewood Electronics, & Langrex, depending of course on what you end up needing. I also use Mouser quite a bit - you can use mouser.co.uk for UK pricing, but they ship ex. USA, with free shipping for orders above a certain amount. All taxes etc. are sorted by Mouser, and it's an excellent fast service (ca. 3 days).

Be very careful with the STV-3H diodes - they are fragile - there's a long thread about them - http://audiokarma.org/forums/index.php?threads/replacing-the-stv-3h-and-4h-diodes.279530/

Alan



ps - which part of Lincolnshire are you ?

 

[glen65]

Thank you both for guidance. I'm getting parts from digikey US and RS components in UK.
The jumpers I mentioned above should I remove them? There is no break on PCB and it's checking fine on continuity.
Also the diodes on the back of board should they still be there?
I have superficial knowledge of electronics and am concerned that previous person may have made some changes upstream and to compensate he may have made these modifications to AWH037? Please guide me

One doesn't necessarily need to be an expert in the field. I would be more concerned about your soldering skills and what you're using to solder and de-solder with as much or more than anything else. That can potentially make the difference between success and failure with a project this extensive.

 

[sajjad amer]

Hi Sajjad, that's bad luck with the eBay purchase - if it's the one I think it is, the internal condition & repairs (for want of a better word) certainly weren't obvious from the listing description.

You might find the following link is a better, more legible, copy of the service manual - http://www.kallhovde.com/pioneer/sa-9900smhires.pdf

A couple of other reliable UK based suppliers would be CPC, Farnell, and eventually Cricklewood Electronics, & Langrex, depending of course on what you end up needing. I also use Mouser quite a bit - you can use mouser.co.uk for UK pricing, but they ship ex. USA, with free shipping for orders above a certain amount. All taxes etc. are sorted by Mouser, and it's an excellent fast service (ca. 3 days).

Be very careful with the STV-3H diodes - they are fragile - there's a long thread about them - http://audiokarma.org/forums/index.php?threads/replacing-the-stv-3h-and-4h-diodes.279530/

Alan



ps - which part of Lincolnshire are you ?

Thank you Alan, this was the only SA-9900 in UK and it was not obvious what condition it was in. I will soldier on and fix it with valuable help from this forum. Thank you for the links as well, very helpful.
I am in Louth , not far from you, if I get stuck may bother you

 

[LesE]

If you need to replace an STV-3H, there is a seller on eBay located in Germany who carries them (item 321845661752).

You will also want to be careful with the AEX-003 posistors which are equally fragile.

 

[sajjad amer]

One doesn't necessarily need to be an expert in the field. I would be more concerned about your soldering skills and what you're using to solder and de-solder with as much or more than anything else. That can potentially make the difference between success and failure with a project this extensive.

I am fairly confident at soldering and de-soldering. My weakness is oscilloscope use but at this moment I am at multi meter stage any way. This is the biggest project so far I have ever undertaken. I hope I have not bitten more than I can chew. Thank you for the support once again, I appreciate it.